V O L U M E 21, NO. 4, A P R I L 1949 Table X. s o . of Samples
523
Classification of Samples of Kapok by Chemical Test (irade-
Y e w Ainterial , No. of '70 of samples sample-
Second-1Iand 1Iaterial s o , of '70 of sample*
iaml,les
0 80
a7
the grade, the lower the buoyancy factor. There is, however, in many cases such a wide variation between the individual samples in the same grade that the tcst is of lit,& value. Of the above determinations, the ammonia, sodium sulfate, and pH were retained while the urea, sodium chloride, oil and fat, and buoyancy were discarded. The standards adopted for the ammonia and sodium sulfate content were 0.0365 and 0.365%, respectively, while the standard chosen for the hydrogen ion concentration of the aqueous extract was 5.15. The number and thc'percentages of the samples v-hich had values below and above these standards are shown in Table IX. All the 41 samples of ne\v kapok (grades 6 to 8) had an ammonia content belon0.0365%, 38 had a sodium sulfate content below 0.365%, and 40 had a pH above 5.15. Of the 59 samples of second-hand kapok (grades 0 to 5 ) ,54 had an ammonia content above 0.036570, 43 had a sodium sulfate content almve 0.365%, mid 53 had a p l l below 5.15. Thus in differentiating between the new or second-haiicl nature of a sample of kapok, the ammonia determination has an over-all accuracy of 95%, the sodium sulfate determination an over-all accuracy of Slyo,and pFI determination an over-all accuracy of 93%. Moskowitz, Landes, and Hiniriiclfarb stated that a sample of kapok should be designated as second-hand if the urea or ammonia content or both are greater than 0.015 and 0.030%, respectively. They pointed out that if the urea mas found in amounts over 0.015%, the ainnionia was always higher than 0.03070 and thus t h e ammonia contcnt alont~is suficicrit t o
differentiate new from second-hand kapok. The results reported in this paper are in substantial agreement with this conclusion. It is, however, desirable to have additional evidence, and for this reason a sample of kapok is not considered, by the authors, t o contain second-hand material unless the ammonia content exceeds 0.0365% and either the sodium sulfate content exceeds 0.365% or the hydrogen ion concentration of the aqueous estract is below 5.15, or both. -4sample of new kapok, removed from it's own pod, had an ammonia content of 0.024% and a sodium sulfate content of 0.24%. ;Is the amount of kapok contained in the pod was insufficient, to do all the tosts, this sample was not included in the list of those reported. The samples of kapok classified as new or secontl-littiid according t o the above criterion are shown in Table S. The 41 samples i n grades 6 to 8 would all be classified as nviv. Of the 35 saniplcs in grades 3 to 5, which consist of the better type of second-hand kapok, 28 would be classified as second-hand and 7 would hc classified as new. These latter samples ivould be classified wrongly, mainly because of their having a substandard aninionia content. Of the 24 samples in grades 0 to 2, 21 would be classified as second-hand and 3 Ivould be classified as new. hlt,hough these latter samples had a high ammonia content, they did riot have either a sodium sulfate content in CSCCSR of 0.365% or a pH value below 5.15. ifying samples of kapok by means of this chemical test, no samples of new material would be classed as second-hand although, i n a fen- cases, second-hand samples would be classed as new. These errors are usually apparent when the sample is graded according to both the physical condition and the intensity of the violet fluorcwxnce eshihitcitl uiidcr ultraviolet light. LITERATURE CITED
(1) Jephcott, C. M.,and Bishop, W.H. I%.,1 x 0 . EN&.CHEX.,AXAL.
ED.,14,400 (1942).
(.7) Moskowitz, S., Landes, W.,and Himmelfaib, D , .4m. Dgestuf Reptr., 25, 220 (1936). R E C L LI D~ 4pril3, 1948
Electrolytic Determination of Copper In Brasses and Bronzes, Tin-Base Alloys, and Aluminum Alloys by Use of
Phosphoric Acid GEORGE XORWITZ. 577 7 7 t h S t . , Brooklyn 9 , By the use of phosphoric acid excellent results can be obtained in the electrodeposition of copper from brasses and bronzes containing tin. The sample is dissolved in 1 to 1 nitric acid without heating, phosphoric acid is added, and the solution is electrolyzed. To determine copper in tin-base alloys, phosphoric acid is added after solution of the sample in hydrochloric and nitric acids, and the solution is heated on the hot plate. The pyrophosphoric acid formed by heating is converted to phosphoric acid by boil-
T
HE use of phosphoric acid has given excellent results in the electrolytic determination of copper in brasses and bronzes, tin-base alloys, and aluminum alloys. COPPER IN BRASSES W D BRONZES
The use of hydrofluoric acid has been suggested by MeKay ( 5 )and Ravner (8)for the electrodeposition of copper from brasses
I%-.
Y.
ing with water, nitric acid is added, and the solution is electrolyzed. Copper is determined in aluminum alloys by dissolving the sample in an acid mixture of phosphoric, sulfuric, and nitric acids by heating strongly on the hot plate, adding water and nitric acid, and electrolyzing the solution. Silica is completely dissolved by the phosphoric and sulfuric acids and does not interfere. The method is not applicable to aluminum alloys containing tin, antimony, bismuth, or silver. and bronzes containing tin. Hydrofluoric acid, however, is an unpleasant reagent to handle, particularly when it must be accurately measured out, and the copper results are high unless the deposits are stripped from the cathode and replated ( 5 ) . Phosphoric acid, a reagent not subject to these objections, will give escelleiit results in electrolysis of copper from all t,ypes of brasses' and bronzes, including those containing tin. The method is simple and rapid.
ANALYTICAL CHEMISTRY
524 Procedure. Transfer 1.0000 gram of the sample to a covered 300-ml. electrolytic beaker, add 20 ml. of 1 to 1 nitric acid, and allow the sample to dissolve without heating. Add 10 ml. of water and 10 ml. of phosphoric acid (857,), and mix by swirling the beaker. Heat to boiling and boil for about 2 minutes to drive off the nitric oxide fumes. Dilute to about 200 ml. with water, and add 2 drops of 0.1 N hydrochloric acid. Electrolyze for 1.5 hours at 2 amperes (and 3 volts), using a platinum gauze cathode (50 mm. in height and 45 mm. in diameter), and a platinum spiral anode. During the electrolysis stir the solution by some suitable means (the author used compressed air). Immerse the cathode in water and then in alcohol, dry it in an oven a t 105' C. for about 3 minutes, cool, and weigh the deposit as metallic copper. The results obtained by the author on several representative brasses and bronzes are shown in Table I.
Table I. Sample 62b" 124aC
Copper i n Brasses a n d Bronzes Copper Present,
Copper Found,
67.396
57.39 57.39 85.00 84.96 88.23 88.20 65.25 65.28 80.21 80.23
%
85.01b
52bd
88.25b
MACE
65,251
YQ
80.211
%
Contains 0.96% tin, 37.97% zinc. b Xational Bureau of Standards certified value. C Contains 4.82% tin, 4.89% lead. d Contains 8.00% tin, 0.72% nickel. * Contain! 4% manganese, 3% iron, 5% aluminum, and 0.01% tin. I Determined b y A.S.T.M. umpire method. Contains 9.1% tin, 8.2% lead, 0.18% antimony, and 0.39% phosphorus a
Solution of the samples in 1 to 1 nitric acid without heating is recommended, because the heavy metastancic precipitate that may form on applying heat is not readily soluble in phosphoric acid. Every brass or bronze the author encountered, except National Bureau of Standards sample 63a, dissolved in a few minutes in 1 to 1 nitric acid without heating. Prolonged heating was required to dissolve this sample, and consequently the proposed method could not be applied. The inapplicability of the method to sample 63a, however, is of no great significance, because this sample is peculiarly machined and has a unique composition (0.11% sulfur, 0.58% phosphorus, 0.49% antimony, 0.027% arsenic, 0.52% iron, etc.). The few flakes 'of metastannic acid that sometimes remain after boiling with phosphoric acid do not affect the accuracy of the determination. The use of an acid mixture of phosphoric and nitric acids to dissolve the samples is not recommended. When such an acid mixture was used, a small amount of undissolved copper (black residue) was sometimes obtained. IXth the method of solution recommended by the author, this difficulty was never encountered. Lead cannot be determined simultaneously with copper, because the electrodeposition of lead is inhibited by the presence of phosphoric acid.
ness usually forms. Heating the solution too long on the hot plate mav result in the formation of difficultly soluble salts. Allow the solution to cool somewhat, add 50 ml. of water, mix by swirling the beaker, heat to boiling, and boil for 10 minutes. Dilute to about 200 ml with water, add 10 ml. of concentrated nitric acid, and stir. Electrolyze the warm solution for 15 minutes a t 2 amperes (and 3 volts), using a platinum gauze cathode (50 mm. in height and 45 mm. in diameter), and a platinum spiral anode. During the electrolysis stir the solution. Immerse the cathode in water and then in alcohol, dry it in an oven a t 105" C. for about 3 minutes, cool, and weigh the deposit as metallic copper. When Xational Bureau of Standards samples 54a and 54b were run in triplicate, the results shown in Table I1 were obtained. The method of the author is shorter and a t least equal in accuracy to the A.S.T.M. electrolytic method which calls for the use of hydrofluoric acid (1). The phosphoric acid prevents the electrolysis of not only tin but also the antimony which tin-base alloys usually contain. Pyrophosphoric acid was ineffective in preventing the plating of the tin (or antimony). This difficulty was overcome by boiling the solution so that the pyrophosphoric acid would be converted to phosphoric acid ( 7 ) . Nitric acid was found essential for the electrolysis. The electrolysis of the copper is so rapid that no trouble a t all is experienced in plating out all the copper in 12 minutes. Electrolysis for more than 20 minutes will lead to some contamination of the copper by tin (or antimony). The proposed method is not recommended for the analysis of tin-base alloys containing silvei or over 0.05% of bismuth. Because of the presence of the phosphoric acid, not much tin or antimony is lost by volatilization, when the hydrochloric and nitric acids are diiven off (3). COPPER IN ALUMLYUM ALLOYS The procedures of Sloviter (IO)and Weinberg (11)for the direct electrolysis of copper in aluminum alloys are not entirely satisfactory for aluminum alloys that contain more than 275 of silicon. In both procedures high results can be caused by mechanical contamination of the copper deposit by the undissolved silicon (9). In the method of Sloviter the sample is dissolved in sodium hydroxide solution, and nitric acid is added. I n the method of Weinberg, the sample is dissolved in a mixture of perchloric and nitric acids. A simple electrolytic procedure for aluminum alloys, which is not subject to silica interference, is proposed. The sample is dissolved in a mixture of phosphoric, sulfuric, and nitric acids by heating strongly on the hot plate ( d ) , water and nitric acid are added, and the solution is electrolyzed
Table 11. Sample
Procedure. Transfer 1.000 gram of the sample to a 300-ml. electrolytic beaker, and add 8 ml. of hydrochloric acid and 8 ml. of nitric acid in that order. After the reaction has ceased, add 15 ml. of 85% phosphoric acid and heat the solution without a cover glass on LL hot plate a t high heat until all the hydrochloric and nitric acid has been driven off. This point is characterized by the following phenomena: The solution changes to very definite blue color, the effervescence ceases, and a very slight cloudi-
b
%
Cu Found,
%
Average C u Found,
%
3.80 3 . 7 6 * 0.03 3.74 3.74 54b b 3.19 3.23 3 . 2 0 * 0.02 3.19 3.19 Contains 88.61% Sn, 7.32 Sb,0.21 P b , 0.02 Bi, 0.04 Fe, and 0.04 As. Contains 87.48% Sn, 7.39 Sb, 1.81 Pb, 0.029 Bi, 0.028 Fe, and 0.052 AB. 54a4
COPPER IN TIN-BASE ALLOYS Attempts to apply the method described above to the determination of copper in tin-base alloys were unsuccessful, because of the large amount of metastannic acid that precipitated on the addition of nitric acid. Further investigation, however, solved the problem.
Copper in Tin-Base Alloys
Cu Present, 3.76
Procedure. Transfer 1.000 gram of the sample to a 300-ml. electrolytic beaker and add 60 ml. of an acid mixture made by mixing 750 ml. of concentrated phosphoric acid, 1000 ml. of concentrated nitric acid, and 250 ml. of concentrated sulfuric acid. Cover the beaker with a watch glass and heat on the hot plate at high heat until a clear solution is obtained. Remove the beaker from the hot plate and allow it to cool somewhat. Dilute to about 200 ml. with water, and add 0 ml. of concentrated nitric acid. Electrolyze for 0.5 hour at 2 amperes (and 3 volts), using a platinum gauze cathode (50 mm. in height and 45 mm. in
V O L U M E 21, NO. 4, A P R I L 1 9 4 9
525
Table 111. Copper in Aluminum Alloys Sample Alcoa 3 2 4 Blcoa 355 Alcoa 1420 Alcoa 3-Sd Alcoa 2-9 85a 86b
Cu Present, %
Cu Found, %
Si Presenta. %
1 . 0 6b 1.35b 3.94b 0.16b 0 . 0 9b 2.488 7.878
1.04 1.34 3.98 0.15 0.11 2.48 7.89
12 5 0.2 0.2 0.1 0.114 0.47
*
Nominal values except 85a a n d 86b.
d
Contajns 2% nickel. Contains 1.2% manganese. National Bureau of Standards certified value.
h Determined by umpire method of Aluminum Co. of Smerica ( d ) . 6
by boiling with water. Insoluble precipitates are sometimes produced when aluminum alloys containing tin, antimony, or bismuth are dissolved in an acid mixture of phosphoric, sulfuric, and nitric acids. Silicides, silica, and elemental silicon are completely dissloved by a mixture of phosphoric and sulfuric acids (4, 6 ) , and the solution remains clear indefinitely even when diluted with water. For the determination of copper in aluminum alloys that COIItain less than 2% silicon the proposed method is neither more nor less accurate than the methods of Sloviter (IO) and \Veinberg(22). LITERATURE CITED
diameter) and a platinum spiral anode. During the electrolysis stir the solution. Immerse the cathode in water and then in alcohol, dry it in an oven a t 105” C. for about 3 minutes, cool, and weigh the deposit as metallic copper. The results obtained by the author on several representative aluminum alloys are shown in Table 111. The proposed method is not recommended for the analysis of aluminum alloys containing tin, antimony, bismuth, or silver, as these elements were found to contaminate the copper deposit. Possibly because of the presence of the sulfuric acid (which is not used in the brass and bronze or tin-base alloy procedures) the copper was contaminated by tin and antimony even when the pyrophosphoric acid had been converted to phoqhoric acid
(1) Am. SOC.Testing Materials, “Methods of Chemical Analysis of M e t a l s , ” ~249, . Philadelphia, Pa., 1946. (2) Churchill, H. V., and Bridges, R. W., “Chemical Analysis of Aluminum,” p. 36, New Kensington, Pa., Aluminum Co. of America, 1941. (3) Hoffman, J. I., and Lundell, G. E. F., J. Research Natl. But. Standards. 22,465 (1939). (4) Lisan. P., and Katz, H. L., ANAL.CHEM.,19, 252-3 (1947). ( 5 ) McKay, L. W., J . Am. Chem. SOC.,36,2375-81 (1914). (6) Norwitz, G., ANAL.CHEM.,20, 182 (1948). (7) Prescott, A. B., and Johnson, 0. C., ”Qualitative Chemical Aiialysis,” p. 493, New York, D. Van Nostrand Go., 1933. (8) Kavrier, H., IND.EXG.CHEM.,ANAL.ED.,17, 41-3 (1945). (9) Scott, W.W., “Standard lMethods of Chemical Analysis,” Vol. I, p. 367, New York, D. Van Nostrand Co., 1939. (10) Sloviter, H. A., IND. ENG.CHEM.,ANAL.ED.,13, 235-6 (1941). (11) Weinberg, S., Ibid., 17, 197 (1945). R E C E I V EDecember D 8, 1947.
Urea Hydrolysis for Precipitating Calcium Oxalate R. S. ISGOLS AND P. E. 3IURRAY State Engineering Experiment S t a t i o n , Georgia School of Technology, Atlanta, G a .
T
HE determination of the calcium ion as calcium oxalate is a well established technique. Willard and Furman ( 3 ) give a method first described by Chan ( 2 ) for precipitating calcium oxalate, and, on a recent lecture tour, Willard presented some of the basic material indicating its advantages. By the older method ( I , 3),the precipitate is formed during the addition of ammonium oxalate and the pH is then raised with ammonium hydroxide. In the new method, acid is added to the sample to produce pH 1.0; then ammonium oxalate and urea are added. The solution must remain clear until the sample is boiled to hydrolyze the urea arid raise the p H t o the point of calcium oxalate precipitation, this may take 10 to 15 minutes. It is evident from Figure 1 that tlie crgrstals precipitated from the hot solution by the hydrolysis of urea are enough larger than those by the old technique to he ready for filtration shortly after formation. This eliminates much of the digestion period needed by the older method and permits a technician to speed up the trst for calcium. hIETHOD
;Inaliquot (100 ml.) of the sample is
laced in an Erlenmeyer flabk. A few drops of methyl red are adxed, then 2.4 ml. of a 1 to I hydrochloric acid solution. this develops a p H of 1.0 which is uccided to prevent preci itaAon of calcium oxalate until desired. Following this, 15 ml. o f a saturated ammonium oxalate solution and 10 grams of urea are added and mixed. The solution must remain clear. The urea must be added dry or as a fresh solution, because even a 24-hour solution contains sufficient ammonium hydroxide to cause precipitation. The solution is heated on a hot plate (generally for 15 minutes) until the methyl red changes color at pH 5.0, and is then ready for filtration. A coarse qualitative paper is used aa the a t e r medium, and, after adequate wash-
ing, the paper plus the precipitate is returned to the original flask or the precipitate may be filtered with vacuum on a small fine filter paper supported by a Gooch crucible. This is somewhat more rapid than the gravity filtration and reduces the amount of paper present in the titrption beaker. The Gooch crucible is returned to the original beaker with the filter paper and precipitate The calcium oxalate precipitate is dissolved with hot sulfuric acid solution and titrated immediately with a standard permanganate solution. A large quantity (5 gallons) of a solution of calcium chloride of known concentration \%asmade up and used as the test solution. S‘arious amounts of magnesium and aluminum sulfates and magnesium chloride were added t o portions of this stock test solution, and a t least ten determinations were made on every portion by the standard and the new techniques. The calcium sulfate solution studies were made on solutions of several batches of chemically pure calcium sulfat,, crystals. RESULTS
-1veruges of ten determinations on each solution by each technique were calculated and the probable error was computed (Table I). There is no significant difference in the concentration of calcium ion from calcium chloride when no other cations or anions are present originally. When a knoxm amount of calcium iulfate is iTeighed out and the calcium ion values are determined, the results by either method do not agree with the theoretical value, but the error is slightly smaller with the urea hydrolysis method than nith the standard procedure. 4 double precipitntion of tlie calcium oxalate from the sulfate solution shows that the sccond precipitation with the standard method fails to yield theoretical values TThile the double precipitation with the urea method does yield theoretical values. Table I1 indicates that
